Technical Field
The present invention relates to a blow-by gas returning apparatus for allowing blow-by gas generated in an engine to flow in an intake passage and return to the engine and, more particularly, to an abnormality diagnosis device configured to diagnose an abnormality of the returning apparatus.
Related Art
Conventionally, there is known, as one example of techniques of the above type, an abnormality diagnosis device for a blow-by gas returning apparatus disclosed in Japanese unexamined patent application publication No. 2009-197676 (“JP-A-2009-197676”). This blow-by gas returning apparatus (Blowby Gas Ventilation Apparatus, which is hereinafter referred to as a “BGV apparatus”) includes a PCV passage (a blow-by gas returning passage) for introducing blow-by gas to a part of an intake passage, located downstream of a throttle valve, and a PCV valve for regulating a flow rate of the blow-by gas in this passage. This abnormality diagnosis device is configured to diagnose whether an abnormality has occurred in at least one of the PCV passage and the PCV valve. Specifically, when the amount of intake air drawn into the engine during ISC control (i.e., during control of an idle rotation speed to a target value) reaches a predetermined amount and no abnormality has not occurred in the BGV apparatus, the abnormality diagnosis device sets, as a first operating state, an engine operating state in which an opening degree of the PCV valve is kept at a first opening degree, and further sets, as a second operating state, an engine operating state in which the opening degree of the PCV valve is kept at a second opening degree different from the first opening degree. The abnormality diagnosis device is configured to determine that an abnormality has occurred in the blow-by gas returning apparatus when a difference between a control amount of the throttle valve under the first operating state set as an actual operating state and a control amount of the throttle valve under the second operating state as the actual operating state during execution of ISC control is equal to or less than a reference value.